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Primary Air

On a recent trip to Haiti I was finally able to construct my CharBowl(tm) charcoal stove. It uses two nested stainless steel bowls (5 quart and 8 quart (4.7 liters and 7.6 liters))for durability and reflectivity with castable insulating refractory between them to reduce conductive heat losses. It has a 6.5" (16.5cm) dia cast iron grate for durability. It has a secondary air pipe to reduce CO emissions and increase heat output. The secondary air outlet pipe is 3/8" (10 mm) nominal (ID 0.493" 12.5mm; OD 0.675", 17mm) black iron with a Tee fitting on top to keep charcoal from dropping into it. 3/4" NC 10 (19mm 2.5) machine threads were cut over the pipe threads. This allowed the use of a split nut and flat washer inside and outside the bowls to hold the bowls together. The elbow is 3/8" to 1/2" . The inlet pipe is nominal 1/2" iron (ID 0.622" 16mm; OD 0.84", 21mm). The bowls sit on a stock pot base for stability and primary air control. (I couldn't get my hands on the stainless pot I really wanted to use for the base. I'm planning to build another with such a base now that I'm back in the States.)
I hope to get some testing done on my second prototype.
It can be used as the base of a TChar stove.

This a low cost simple tin can of less $ 0.5 , with primary and secondary air facility to use for efficient camp fires and also for cooking on it. One need to strive for using the best and efficient stoves, but for the poor, and unavoidable situation / emergencies, such simple tools can be used.
This design is incidental, I have prepared lots of tin cans for Magh CL stove http://e-mcl.blogspot.com/, this winter it had been too cold, during the nights for warmth these tins were used, the efficiency was very high as compared to the open campfires and it was comfortable to use it everywhere. The primary and secondary air helped in complete combustion. Using it for cooking from camp fire mode was also convenient, by just putting on top a concentrator slab and pot rest. During cooking the fuel was fed from the side openings. The wood fed is vertical to slant, this helped in convenient combustion. While cooking was done the radiation of heat was enough for warmth.

I learned to make TLUDs from Dr. Paul Anderson when he came to do a stove & biochar demonstration for Biochar Ontario in June 2009. Since my primary interest was in producing biochar, I went home and began building a larger version of the “Champion” TLUD stove from a 55 gallon drum and a 25 gallon drum (pictured above.) I have been following this list since then and on “Dr. TLUD’s” urging, I thought should begin sharing with this community what I have been learning.

The “Large TLUD”

Essentially a "beefed up" version of the Champion TLUD Stove, my large TLUD has worked beautifully from the first trial run. The pyrolysis process is extremely clean in terms of visible emissions and can produce 25 – 30 liters (6 – 8 gallons) of biochar per run depending on feedstock. To halt the pyrolysis process to retain the biochar I have always used a watering can to quench the glowing coals. Two to four gallons of water usually does the trick.

Using this stove, I have pyrolyzed a number of different types of feedstock including: scraps of spruce lumber, pine needles, pine cones, pine bark, corn cobs, chicken litter, and hardwood sawdust pellets. The successful pyrolysis of the various feedstock has always depended on (no surprise here) having dry feedstock with pyrolysis times ranging from one to two + hours (again, depending on feedstock.)

Until recently I had been using a hardware store woodstove thermometer on the top of the stove.
I estimated pyroloysis temperatures to be in the 350-450 C range. I began using a 12vdc computer cooling fan to shorten run times and boost temperatures closer to 500 C. I recently acquired a temperature data logger and found, to my surprise, that temperature quickly shot to over 800 C with the fan. Even without the fan, temperatures in and above the pyrolysis front were between 600 and 750 C. The data from the first run with the data logger is attached. *Note:T1 is the thermocouple near the top of the inner fuel barrel just below the top of the feedstck and T2 is the thermocouple about 2 inches above the bottom of the inner fuel barrel.

My next steps are to monitor temperatures while experimenting with choking the primary air to different degrees and as I gain better control of pyrolysis temperatures, to (further) experiment with various types of feedstock. I am also working on a simple system to use the pyrolysis heat to dry feedstock.
I will post my results here.

[MAGH OPEN STOVE](http://e-maghopenstove.blogspot.com/) is an institutional fixed woodgas stove. This stove is useful for cooking needs of up to 100. With primary and secondary air controls it is easy to operate and highly efficient. For making this stove, "Magh CM" stoves are used inside. This stove is installed at "Open House", Hyderabad, a place for destitute youth for cooking their own food, shelter, studies, etc. Implemented under the "Good Stoves and Biochar Communities" Project, Implemented by GEO with support of GoodPlanet.org France. Stove design by Dr. N. Sai Bhaskar Reddy. For more details visit http://e-maghopenstove.blogspot.com/

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